Communication apparatus, integrated circuit, and communication method

ABSTRACT

A communication apparatus repeatedly outputs a first multi-carrier signal SS during predetermined periods T 1 , T 2 , T 3 , . . . , and outputs a second multi-carrier signal RS whose phase vector is different from that of the first multi-carrier signal SS, at a predetermined timing based on the first multi-carrier signal SS. The communication apparatus further detects the second multi-carrier signal RS output from another communication apparatus, which uses a different communication method from the communication apparatus. Accordingly, both communication apparatuses can differentiate the first multi-carrier signal SS from the second multi-carrier signal RS without performing relatively cumbersome modulation and other processes.

This is a divisional application of application Ser. No. 11/545,779filed Oct. 11, 2006, which is based on Japanese Application No.2005-297529 filed Oct. 12, 2005, and Japanese Application No.2006-114191 filed Apr. 18, 2006, the entire contents of each which areincorporated by reference herein.

INCORPORATION BY REFERENCE

This application is related to the following patent which is herebyincorporated by reference in its entirely: U.S. Pat. No. 6,944,232,RECEIVING APPARATUS AND METHOD FOR DIGITAL MULTI-CARRIER TRANSMISSION,Inventors: Hisao Koga et al., filed on Feb. 19, 2004.

BACKGROUND

1. Field of the Invention

The present invention relates to a communication apparatus, anintegrated circuit and a communication method that are capable of easilydetecting signals output from other communication apparatuses, which usedifferent communication methods and are connected to a commontransmission line, while avoiding interference between signals withoutperforming relatively cumbersome modulation and other processes.

2. Description of Related Art

With the recent development of communication technology, PLC (Power LineCommunication) has been gaining attention. PLC is a technology thatperforms multi-carrier communications among a plurality of terminalapparatuses, using power lines installed indoors as transmission lines,and utilizes an OFDM (Orthogonal Frequency Division Multiplexing) system(e.g., Japanese Patent Laid-Open Publication 2000-165304). OFDM is amodulation method for multi-carrier data transmission, by which aplurality of carriers are transmitted in a multiplex way on a frequencyaxis. OFDM uses an FFT (Fast Fourier Transform) or a DWT (DiscreteWavelet Transform) to narrow frequency intervals of multi-carriers andto closely space a plurality of carriers in such a way that theypartially overlap and yet do not interfere with one another. OFDM thusenables broadband transmission by efficiently using a narrow frequencyspectrum.

For multi-carrier communications, such as power line communications, atechnology is proposed to suppress interference in such manner that aphase vector flattens time waveform levels to prevent occurrencesignificant peak. In this technology, when a time waveform has nosignificant peak, the phase of each sub-carrier is rotated using thephase vector of default. However, when the significant peak is detected,the phase vector is changed until a phase vector that generates nowaveform peak is found, and the phase of each sub-carrier is thusrotated according to the changed phase vector (Denis J. G. Mestdagh andPaul M. P. Spruyt, “A Method to Reduce the Probability of Clipping inDMT-Based Transceivers”, IEEE Transactions on Communications, Vol. 44,No. 10, pp. 1234-1238, 1996). Such a technology for suppressing peaks isessential for reducing the design difficulty for a power amplifier formulti-carrier communications.

Usually, when the specifications of the same communication method areused, the specifications of communication apparatuses connected to eachnetwork are generally common even for a case where different logicalnetworks are formed using a network key, or the like. This way, thecommunication apparatuses can detect (carrier sense) signals transmittedbetween different networks, on a physical layer level of thecommunication apparatuses, and it is possible to prevent interferencebetween signals using a CSMA (Carrier Sense Multiple Access), thusenabling smooth communication even for relatively closely locateddifferent networks.

However, different manufacturers may use different specifications for acommunication method such as a communication protocol, a modulationscheme and a frequency band. Such communication technology is highlylikely to be used in an environment where a plurality of types ofcommunication methods are mixed in the same location. For instance,users (communication apparatus users) in collective housing such as anapartment or a condominium do not necessarily use communicationapparatuses (e.g., modems) of the same manufacturer. in this case, aplurality of types of communication apparatuses independently made by aplurality of manufacturers may be simultaneously connected to a commonpower line.

When the a plurality of types of communication apparatuses are connectedto the common power line, a communication apparatus cannot demodulate asignal transmitted from a different communication apparatus using adifferent type of communication method. Therefore, such a signal isacknowledged merely as noise. Accordingly, although the plurality oftypes of communication apparatuses use the same frequency band, even theexistence of other communication apparatuses is not acknowledged. Thiscauses interference between signals transmitted from the plurality oftypes of communication apparatuses, thereby causing communicationerrors. In other words, the plurality of types of communicationapparatuses sometimes cannot coexist on the common power line.

On the other hand, when each communication apparatus is set up toperform modulation, signals transmitted from other communicationapparatuses can be differentiated. However, modulation processesperformed to allow the plurality of types of communication apparatusesto coexist have an adverse effect of increasing the workload.

SUMMARY

An object of embodiments described in the following is to provide acommunication apparatus, an integrated circuit and a communicationmethod that are capable of easily detecting signals output from othercommunication apparatuses, even when a plurality of types ofcommunication apparatuses using different communication methods areconnected to a common transmission line, without performing relativelycumbersome modulation and other processes.

A first communication apparatus, which is described in the embodiments,is a communication apparatus is capable of connecting to a power lineconnected to at least a first communication apparatus and a secondcommunication apparatus. The first communication apparatus is capable ofperforming a data transmission with said communication apparatus. Thesecond communication apparatus is incapable of performing the datatransmission with said communication apparatus. The communicationapparatus includes a receiver, a carrier detector, a channel settingunit and a transmitter. The receiver receives a signal from the secondcommunication apparatus. The carrier detector detects a predetermineddata in the signal. The channel setting unit sets at least one of timeslot and frequency band used for the first communication apparatus whenthe carrier detector detects the predetermined data, the time or thefrequency band used for the first communication apparatus beingdifferent from a time or a frequency band used for the secondcommunication apparatus. The transmitter performs the data transmissionwith the first communication apparatus in at least one of the time andthe frequency band used for the first communication apparatus.

An integrated circuit, which is described in the embodiments, is anintegrated circuit is capable of connecting to a power line connected toat least a first communication apparatus and a second communicationapparatus. The first communication apparatus is capable of performing adata transmission with said integrated circuit. The second communicationapparatus is incapable of performing the data transmission with saidintegrated circuit. The integrated circuit includes a receiver, acarrier detector, a channel setting unit and a transmitter. The receiverreceives a signal from the second communication apparatus. The carrierdetector detects a predetermined data in the signal. The channel settingunit sets at least one of time and frequency band used for the firstcommunication apparatus when the carrier detector detects thepredetermined data, the time or the frequency band used for the firstcommunication apparatus being different from a time or a frequency bandused for the second communication apparatus. The transmitter performsthe data transmission with the first communication apparatus in at leastone of the time and the frequency band used for the first communicationapparatus.

A communication method, which is described in the embodiments, is acommunication method controls data transmission that a communicationapparatus performs through a power line connected to at least a firstcommunication apparatus and a second communication apparatus. The firstcommunication apparatus is capable of performing the data transmissionwith said communication apparatus. The second communication apparatus isincapable of performing the data transmission with said communicationapparatus. The communication method includes: receiving a signal fromthe second communication apparatus; detecting a predetermined data inthe signal; setting at least one of time and frequency band used for thefirst communication apparatus when the carrier detector detects thepredetermined data, the time or the frequency band used for the firstcommunication apparatus being different from a time or a frequency bandused for the second communication apparatus; and performing the datatransmission with the first communication apparatus in at least one ofthe time and the frequency band used for the first communicationapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view of a communication systemaccording to a first embodiment;

FIG. 2 (a) is an external perspective view of a front side of a modem;

FIG. 2 (b) is an external perspective view of a rear side of the modem;

FIG. 3 is a block diagram illustrating a hardware example thatconstitutes the modem according to the first embodiment;

FIG. 4 is a functional block diagram of a PLC PHY block;

FIG. 5 shows a signal format of an OFDM signal;

FIG. 6 shows a signal spectrum of the OFDM signal;

FIG. 7 (a) is a time chart that employs time division;

FIG. 7 (b) is a time chart that employs another example of timedivision;

FIG. 7 (c) is a time chart that employs frequency and time division;

FIG. 8 (a) shows an example of attenuation-frequency characteristics ona power line;

FIG. 8 (b) shows an example of noise level-frequency characteristics onthe power line;

FIG. 9 shows time slots corresponding to request signals transmittedduring control periods;

FIG. 10 is a time chart illustrating exchange of control signals betweenmodems;

FIG. 11 is a block diagram illustrating a hardware example thatconstitutes a modem according to a second embodiment;

FIG. 12 (a) is a time chart that employs frequency division;

FIG. 12 (b) is a time chart that employs frequency and time division;

FIG. 13 is a time chart illustrating an operation example of a pluralityof modems, when different request signals are transmitted;

FIG. 14 is a time chart illustrating an operation example of theplurality of modems, when some communication methods are not in syncwith synchronization signals;

FIG. 15 is a block diagram illustrating a hardware example thatconstitutes a modem according to a third embodiment;

FIG. 16 is a functional block diagram of a PLC PHY block of a sub IC;

FIG. 17 is a time chart illustrating an operation example of a pluralityof modems according to the third embodiment;

FIG. 18 is a flowchart illustrating a process of detecting a requestsignal;

FIG. 19 shows time slots corresponding to request signals according to afourth embodiment;

FIG. 20 is a flowchart illustrating a process of detecting a requestsignal according to the fourth embodiment;

FIG. 21 is a time chart illustrating an operation example of a pluralityof modems according to a fifth embodiment; and

FIG. 22 is a flowchart illustrating a process of modifying a phasevector according to the fifth embodiment.

DETAILED DESCRIPTION

First Embodiment

The first embodiment is described in the following with reference toFIGS. 1 to 10.

FIG. 1 is a schematic configuration view of communication system 100according to the first embodiment. As shown in FIG. 1, communicationsystem 100 includes a network using power lines 2 as transmission lines.Power lines 2 include: power transmission cables of power pole 7, whichis provided outdoors; a pull-in cable connected to the powertransmission cables via transformer 4; and an interior wiring withinresidence 1. Power lines 2, which include the power transmission cables,are connected to power distribution panel 6 via power lines 2, whichinclude the pull-in cable. Fiber cable 8, which is connected to an ISP(Internet Service Provider/not shown), or the like, is connected topower distribution panel 6 via modem 10C3, which functions as acommunication apparatus.

Power lines 2, which are connected to power distribution panel 6, areconnected to a plurality of outlets 5 installed in residence 1. Aplurality of modems using different types of communication methods areconnected to outlets 5 via plugs 3 and power lines 2 (e.g., VVF cables).Power lines 2 feed commercial AC voltage (e.g., 100V, 60 Hz (or 50 Hz))to various electric appliances, although values other than 100V, 60 Hzcan also be used. For instance, an AC voltage of 120V, 60 Hz is used inthe U.S. and an AC voltage of 110/220V, 50 Hz is used in China, etc.

As shown in FIG. 1, modems 10A1, 10A2 and 10A3 use communication methodA; modems 10B1 and 10B2 use communication method B; and modems 10C1,10C2 and 10C3 use communication method C. All of the modems areinstalled in residence 1. Various electric appliances are connected tothe respective modems via LAN cables 9. More specifically, intercom 109is connected to modem 10A1; and telephone with display 107 and 107 areconnected to modems 10A2 and 10A3. Television 102 is connected to modem10B1; and server 105 is connected to modem 10B2. Portable personalcomputer (hereinafter simply referred to as a PC) 101 is connected tomodem 10C1; and television 106 is connected to modem 10C2.

In the following description, when no particular distinction isnecessary among modems 10A1, 10A2, 10A3, 10B1, 10B2, 10C1, 10C2 and10C3, these modems are all simply referred to as “modem 10”. The modemdescribed in the present embodiment is an example of communicationapparatus 10. Any device having a communication function, other than amodem, can also be used. For instance, electric appliances having amodem function (more specifically, various electric appliances 101, 102,103, . . . shown in FIG. 1) can also be used.

In the specification, power line communication used only in housings,e.g., residences and collective housings, and other structures, e.g.,factories and buildings, is defined as “in-home communication”; andpower line communication (including communication methods used inbuildings using such power line communication) used for outdoor powertransmission cables and fiber cables is defined as “accesscommunication”. In the following, a communication system by in-homecommunication is simply referred to as an “in-home system”; and acommunication system by access communication is simply referred to as an“access system”. In FIG. 1, a communication system including modems10A1, 10A2, 10A3, 10B1 and 10B2 belongs to the in-home system; and acommunication system including modems 10C1, 10C2 and 10C3 belongs to theaccess system.

FIG. 2 (a) is an external perspective view of a front side of the modem;and FIG. 2 (b) is an external perspective view of a rear side of themodem. Modem 10 has chassis 11 shown in FIG. 2. Displays 16, such as LED(Light Emitting Diodes), are provided on the front of chassis 11. Powerconnector 12, LAN (Local Area Network) modular jack 13, such as RJ 45and D-sub connector 15 are provided on the rear of chassis 11. Powerlines 2, such as a parallel cable, are connected to power connector 12.LAN cable 9 is connected to modular jack 13. A D-sub cable (not shown)is connected to D-sub connector 15.

FIG. 3 is a block diagram illustrating a hardware example thatconstitutes modem 10 according to the first embodiment. As shown in FIG.3, modem 10 includes circuit module 20 and switching regulator 50.Switching regulator 50 feeds various levels of voltage (e.g., +1.2V,+3.3V, +12V) to circuit module 20. Circuit module 20 includes main IC(Integrated Circuit) 22, AFE IC (Analog Front End IC) 23, band-passfilter 25, driver IC 26, coupler 27, band-pass filter 29, AMP(amplifier) IC 30, band-pass filter 31, ADC (AD converter) IC 32, memory33 and Ethernet PHY IC 12. Power connector 12 is connected to powerlines 2 via plug 3 and outlet 5.

Main IC 22 includes: CPU (Central Processing Unit) 22A, PLC MAC (PowerLine Communication Media Access Control layer) block 22C and PLC PHY(Power Line Communication Physical layer) block 22B. CPU 22A is equippedwith a 32-bit RISC (Reduced Instruction Set Computer) processor. PLC MACblock 22C controls a MAC layer; and PLC PHY block 22B controls a PHYlayer. AFE IC 23 includes DA converter (DAC) 23A, variable gainamplifiers (VGAs) 23B and 23C, and AD converter (ADC) 23D. Coupler 27includes coil transformer 27A, and coupling condensers 27B and 27C.

Circuit module 20 further includes sub IC 42, AFE IC 43, band-passfilter 45, driver IC 46 and band-pass filter 49. Sub IC 42 includes PLCMAC block 42C and PLC PHY block 42B. AFE IC 43 includes DA converter(DAC) 43A, variable gain amplifiers (VGAs) 43B and 43C and AD converter(ADC) 43D.

Main IC 22, as with a general modem, is an electric circuit (LSI) thatperforms signal processing including basic control andmodulation/demodulation for data communication. In other words, main IC22 modulates received data, which are output from a communicationterminal such as a PC, and outputs as a transmitted signal (data) to AFEIC 23. Main IC 22 also demodulates transmitted data, which are input viaAFE IC 23 from power lines 2, and outputs as a received signal (data) toa communication apparatus such as a PC. Main IC 22 further outputs apredetermined communication request signal to sub IC 42 prior to thedata communication, so as to check if power lines 2 can be used.

Driver IC 26 functions as a switch that blocks/passes transmitted andreceived signals between main IC 22 and power lines 2. In other words,driver IC 26 serves as an interface between a digital signal processingcircuit and the power lines; and the data communication can becontrolled by switching ON/OFF driver IC 26. Driver IC 26 can take anyform of configuration, as long as it has control capabilities toallow/deny the data communication. For instance, driver IC 26 can beequipped with a switch, such as an analog switch, which enables ON/OFFcontrol by an external signal.

A first signal output unit, a second signal output unit and a phasevector setting unit are provided as PLC PHY block 42B of sub IC 42respectively. A data communication range setting unit is provided as PLCPHY block 22B, and band-pass filters 25 and 29. A data communicationunit is provided as PLC PHY block 22B and AFE IC 23. PLC PHY block 42Bis a sample of a receiver, a carrier detector, and a transmitter.

FIG. 4 is a functional block diagram of PLC PHY block 42B of sub IC 42.First, a phase setting process, which uses an inverse wavelet transformfor a multi-carrier signal modulation, is described with reference toFIG. 4.

PLC PHY block 42B, as shown in the lower section of FIG. 4, includes:symbol mapper 406 that maps transmitted data as serial data onto acomplex coordinate plane; S/P converter 407 that converts the serialdata into parallel data corresponding to respective sub-carriers of amulti-carrier; phase rotator 408 that rotates each of phases of theparallel data; inverse wavelet transformer 410 that performsmulti-carrier modulation by performing inverse wavelet transform on thephase-rotated parallel data; and controller 405 that controls the phasevectors rotated by phase rotator 408. Phase vector is a set of valuesthat indicate phases corresponding to respective sub-carrier signals ina multi-carrier signal. The phase vector is the set of values forflattening time waveform levels to prevent occurrence significant peak.The signal phases of all the sub-carriers are randomly set, so that timewaveform levels produce no peak. Accordingly, as the phase of eachsub-carrier signal is randomized, the time waveform levels areflattened, thus producing no peak.

Symbol mapper 406 performs a first modulation in which transmitted datain the form of bit data are converted into symbol data, with a total ofM−1 sub-carriers mapped onto the complex coordinate plane. S/P converter407 converts sequentially input serial data (transmission symbols)generated through the first modulation, to be sequentially input, intoparallel data corresponding to each of the sub-carriers in themulti-carrier signal. Then, phase rotator 408 rotates the phases of theinput parallel data. In this case, a (2n−1)^(th) input (n is a positiveinteger) is considered as the in-phase component of the complex data,while a 2n^(th) input is considered as the orthogonal component (suppose1≦n≦M/2−1) of the complex data. The numbers of sub-carriers areconsidered as 0˜M−1. Complex sub-carriers are made of sub-carrier pairs,and the phase of each of the sub-carriers is rotated. In this example,the maximum number of parallel data (number of sub-carriers) to bephase-rotated is M/2−1. Inverse wavelet transformer 410 performsmulti-carrier modulation through the inverse wavelet transform of thephase-rotated parallel data of each sub-carrier, generating thetransmitted signals in the multi-carrier. The SIP converter can be usedbefore the symbol mapper.

Controller 405 supplies a signal that controls a phase vector(hereinafter simply referred to as a “vector control signal”) to phaserotator 408, controlling settings and changes of the phase vector. inthis example, controller 405 may include a random value generator. Therandom value generator generates a random value using, for example, a PN(Pseudo Noise) sequence and supplies the random value to phase rotator408 as a vector control signal in order to perform phase rotation oneach of its targeted sub-carriers. As such random values mentionedabove, two values, i.e., 0 and π (or −1) are generated. Or, controller405 may include a cyclic shift designator so that a vector controlsignal (a phase shift value) for a cyclic shift operation is generated;the vector control signal to phase rotator 405 is supplied; and phaserotation on each of the sub-carriers to be used for the communication isperformed.

As described above, since phases are rotated based on the PN sequence,phase vectors having a less time correlation can be set, so that firstand second signals can be differentiated with more accuracy.Particularly, using an M sequence as the PN sequence enables a settingof phase vectors having coherent auto-correlation (coherent phases),thereby achieving more accurate differentiation. Any sequence may beused to perform phase rotation as long as it has self correlation issensitive and mutual correlation is insensitive. For example, PNsequence such as M sequence and Gold sequence may be used to perform thephase rotation.

Instead of rotating each of targeted sub-carriers each time, it is alsopossible to pre-save, in a medium such as a memory, output signalsthemselves from phase rotator 408 or inverse wavelet transformer 410,and to retrieve the signal from the memory as a given data signal eachtime a vector control signal is generated, so as to output the generatedvector control signal as a vector control signal. Or, it is alsopossible to retrieve given data each time a phase vector is changed, andoutput the given data as a vector control signal.

The following describes a phase re-rotation process, which uses thewavelet transform for modulating the multi-carrier signal. PLC PHY block42B, as indicated in the upper section of FIG. 4, further includes:wavelet transformer 401 that performs multi-carrier demodulation throughthe wavelet transform of a received signal; phase rotator 402 thatrotates phases of parallel data corresponding to each of modulatedsub-carriers; and P/S converter 403 that converts the parallel datacorresponding to each of the phase-re-rotated sub-carriers into serialdata.

Wavelet transformer 401 demodulates the multi-carrier signal through thewavelet transform of the received signal, and generates parallel datacorresponding to each of the sub-carriers in the multi-carrier. Phaserotator 402 re-rotates the parallel data individually by rotating thephases of the input parallel data. Then, P/S converter 403 converts theinput parallel data, each packet of which corresponds to each of thesub-carriers in the multi-carrier, into serial data so as to obtain thereceived data. Changing the order of phase rotator 402 and P/S converter403 causes no operational difficulties.

Controller 405 controls settings and changes of a phase vector bysupplying a vector control signal to phase rotator 402. As with theabove-described phase setting process, controller 405 includes a randomvalue generator, which generates a random value using the PN (PseudoNoise) sequence, for instance, and supplies the generated random valueas a vector control signal to phase rotator 402, in order to rotate eachof the targeted sub-carriers. As such random values mentioned above, twovalues, i.e., 0 and π are generated. Or, controller 405 may include acyclic shift designator so that a vector control signal (a phase shiftvalue) for a cyclic shift operation is generated; the vector controlsignal to phase rotator 402 is supplied; and phase rotation on each ofthe sub-carriers to be used for the communication is performed.Accordingly, such a cyclic shift operation enables a large number ofsub-carriers to be phase-rotated with relatively light workload.

In the first embodiment, an OFDM signal is used as a data signal or acontrol signal (described later). FIG. 5 shows a signal format of anOFDM signal. FIG. 6 shows a signal spectrum of the OFDM signal. The OFDMsignal is configured the same way as a preamble signal, which is usuallyused for carrier detection and synchronization processes. The preamblesignal includes a predetermined data. For instance, controller 405inputs , as the predetermined data, a series of the same value for eachsub-carrier (e.g., a signal in the form of 1,1,1, . . . for eachsub-carrier) into phase rotator 408; rotates each of the sub-carriers byan appropriate phase vector; and generates a time signal throughfrequency-time transform at inverse wavelet transformer 410. As anactual OFDM signal, a multi-tone signal with a symbol length ofapproximately 100 μs (e.g., 56 waves) is used for instance.

Although descriptions have been provided above for the case where aphase vector is rotated through the wavelet transform, othertransformation methods, such as a Fourier transform, can also be used.Phase setting and re-rotation processes of PLC PHY bock 22B areidentical to those of PLC PHY block 42B, and their descriptions are thusomitted.

FIG. 7 (a) is a time chart that employs time division; FIG. 7 (b) is atime chart that employs another example of time division; and FIG. 7 (c)is a time chart that employs frequency and time division.

In the first embodiment, frequency bands on power lines 2 are divided,as shown in FIG. 7, into control signal band BW1 and data signal bandBW2. Control signal band BW1 is a band for transmitting a controlsignal. The control signal is for controlling communication betweenmodems 10, which includes a synchronization signal SS and a requestsignal RS, the synchronization signal SS indicating a synchronizationtiming for each modem 10, and the request signal RS announcing that eachmodem 10 starts data communication. The request signal RS is an exampleof the first signal; and the synchronization signal SS is an example ofthe second signal.

Data signal band BW2 is a band for transmitting a data signal. The datasignal contains various information, such as video image, voice, andtext data, which is specified in the payload of a packet. When afrequency band used for the power line communication is between 2 and 30MHz, for instance, a frequency band of 2-3 MHz is assigned as controlsignal band BW1; and a frequency band of 3-30 MHz is assigned as datasignal band BW2. Although an arbitrary frequency band can be selected ascontrol signal band BW1, lower frequencies allow sampling frequencies tobe lowered, thereby enabling the modem to be configured with a simplecircuit.

FIG. 8 (a) shows an example of attenuation-frequency characteristics onthe power line; and FIG. 8 (b) shows an example of noise level-frequencycharacteristics on the power line. As shown in FIG. 8 (a), signalattenuation is high in the frequency band of 2-3 MHz, resulting in ahigher noise level as shown in FIG. 8 (b). To achieve high-speedtransmission, it is preferable that the communication uses as broadfrequency band as possible. However, as described above, a noise levelincreases concomitantly with an attenuation level in the frequency bandof 2-3 MHz, and an S/N (signal-to-noise ratio) thus decreases, therebymaking only a limited contribution to high-speed transmission.Therefore, the reduction of transmission speed can be kept to a minimumby allocating the frequency band of 2-3 MHz exclusively to negotiationsas control signal band BW1. This also enables the use of a relativelyhigher frequency band for data transmission, thereby improving its datatransmission efficiency.

The following describes a specific control operation performed by PLCPHY block 42B of sub IC 42 shown in FIG. 3, the control operationallowing a plurality of modems 10 to coexist on the common power lines2.

In the first embodiment, two or more different types of phase vectors,which use the same specifications (e.g., a sampling frequency and symbollength) of a control signal, are used as a control signal common to aplurality of types of modems 10. For instance, various types of phasevectors, such as a phase vector exclusively used for a synchronizationsignal SS and a phase vector exclusively used for a request signal RS,are used as needed, so as to control the a plurality of types of modems.

More specifically, PLC PHY block 42B of sub IC 42 transmits apredetermined signal to driver IC 26, so that driver IC 26 blocks datacommunication at main IC 22. When driver IC 26 is turned OFF, PLC PHYblock 42B outputs a synchronization signal SS via AFE IC 43, band-passfilter 45 and driver IC 46. The synchronization signal SS issuperimposed to AC power by coupler 27, and output to power lines 2 viapower connector 12, plug 3 and outlet 5. A synchronization signal SS isset to be output during each predetermined time period; and PLC PHYblock 42B repeatedly outputs a synchronization signal SS in eachpredetermined cycle.

As shown in FIG. 7 (a), PLC PHY block 42B of modem 10B1 (see FIG. 1),which uses communication method B, outputs a synchronization signal SSat times t1, t9, t11, t20, t30, . . . . As previously described, sincetwo or more types of phase vectors are used, each modem 10 stores, inits predetermined memory (not shown), data (two values, i.e., 0 and πfor each sub-carrier) related to phase vectors of a control signal, suchas a synchronization signal SS and a request signal RS. Therefore, PLCPHY block 42B of each modem 10 retrieves, from its memory, data relatedto the phase vectors, and detects a synchronization signal SS afterexecuting the above-described phase re-rotation process at phase rotator402 and controller 405. By detecting a synchronization signal SS, eachmodem 10 sets control periods T1, T2, T3, T4, . . . , each of whichdefines a predetermined cycle (e.g., ms order) as one cycle. A periodfor transmitting a control signal, as described above, is referred to as“control period Tc”.

FIG. 9 shows time slots corresponding to request signals transmittedduring control period Tc. PLC PHY block 42B of each modem 10 isconfigured to output a request signal RS after a period corresponding toits own communication method has passed based on where a synchronizationsignal SS was detected. Phase rotator 408 and controller 405 execute theabove-described phase setting process, so that the phase vector of therequest signal RS is different from that of the synchronization signalSS.

As shown in FIG. 9, for instance, it is assumed that modem 10B1 outputsa synchronization signal SS between times t1 and t2. In this case,modems each of 10A1, 10A2 and 10A3, which uses communication method A,outputs a request signal RS after the time has passed from times t1 tot2. Modems 10B1 and 10B2, which use communication method B, output arequest signal RS after the time has passed from times t1 through t3.Modems 10C1 and 10C2, which use communication method C, output a requestsignal RS after the time has passed from times t1 through t4. In otherwords, time slots T12, T13, T14, . . . , T18, which correspond tocommunication methods A, B, C, . . . , are set during control period Tc.A period set for each time slot does not need to be at equal intervals.

Each modem 10 stores in its predetermined memory data related to thephase vector of a request signal RS. Therefore, as with the case for asynchronization signal SS, each modem 10 retrieves, from its memory,data related to the phase vector, and detects the request signal RSafter executing the phase re-rotation process at phase rotator 402 andcontroller 405. The request signal RS, as previously described, is setby phase rotator 408 so that its phase vector is different from that ofthe synchronization signal SS. Therefore, each modem 10 candifferentiate the request signal RS from the synchronization signal SSbased on the differences of their phase vectors.

When the same phase vector is used for a synchronization signal SS and arequest signal RS, and when a carrier detection is performed usingsignals output from wavelet transformer 401, for instance, usingcorrelations between carriers and a distribution of correlation valuesin a frequency domain, both signals become receivable, thereby making itimpossible to tell whether the synchronization signal SS or the requestsignal RS has been transmitted. The power line communication apparatus,however, operates controller 405 to perform a carrier detection usingthe phase vector used for the synchronization signal SS, as well asperforming a carrier detection using the phase vector used for therequest signal RS. In this manner, two different phase vectors are usedfor two different signals, and it has thus become impossible tosimultaneously perform carrier detections for a plurality of signals ina frequency domain. This enables differentiation between thesynchronization signal SS and the request signal RS, which allows eachmodem 10 to acknowledge what a control signal signifies.

Each modem 10 stores, in its predetermined modem (not shown in thefigure), data related to a correlation between a time slot and acommunication method. Based on the correlation, it is possible to detectin which time slot during one control period Tc a request signal RS isoutput, and thus to know the number of communication methods (namely,the number of types of communication methods) of modems that haveannounced initiation of data transmission.

As described above, since each request signal RS is output in itscorresponding time slot T12, T13, . . . , T18, interference betweenrequest signals RS can be prevented. As a result, each modem 10 canreliably detect request signals RS output from other modems 10. When acorrelation between a time slot and a communication method ispredetermined, the order of outputting a request signal RS is notlimited to A→B→C→ . . . , but can be changed as needed. Time slots T12,T13, . . . , T18 do not need to be at equal intervals.

In addition, when a control signal is output to each of the time slotsduring control period Tc, any functional signification is possible foreach slot. For instance, it is possible to use a specific time slotduring control period Tc (e.g., time slot T18) as a special time slotfor allowing a plurality of modems to coexist by employing frequencydivision.

The following describes an example of a specific operation performed bymodem 10 according to the first embodiment with reference to FIGS. 1, 3,7 (a), 9 and 10. FIG. 10 shows a timing chart illustrating exchange ofcontrol signals between modems 10. In this example, modem 10B1, whichuses communication method B, outputs synchronization signals.Descriptions are provided for transmission of control signals frommodems 10A1, 10B1 and 10C1 only, to facilitate understanding of theembodiment.

As shown in FIGS. 7 (a), 9 and 10, modem 10B1 outputs, to power lines 2,synchronization signals SS at time t1. PLC PHY block 42B of each modem10 monitors the status of all the time slots, i.e., T12, T13, . . . ,T18 during control period Tc; therefore, other modems 10A1 and 10C1detect the synchronization signals SS output from modem 10B1. Here, itis assumed that the signal of a video image captured by intercom 109(see FIG. 1) is transmitted to modem 10A1 via LAN cable 9. Modem 10A1outputs, to power lines 2, request signals RS at time t2, so as tooutput the received signal of the video image to display telephone 103(see FIG. 1) via modem 10A2. Other modems 10B1 and 10C1 detect therequest signals RS output from modem 10A1. The request signal RS and thesynchronization signal SS transmitted to modem 10A2 are not describes inFIG. 10.

Modems 10B1 and 10B2, which use communication method B, and modems 10C1,10C2 and 10C3, which use communication method C, do not perform datacommunication between times t3 and t9, and therefore output no requestsignal RS as shown in FIGS. 7 (a) and 9. Since modem 10A1 monitors for arequest signal RS in time slots T12, T13, . . . , T18, and detects norequest signal RS, modem 10A1 performs data communication using thefollowing entire control period Tc (T2).

When modem 10B1 outputs to power lines 2 synchronization signals SS attime t9, main IC 22 of modem 10A1 (see FIG. 3) outputs a communicationrequest signal to sub IC 42 (see FIG. 3). Upon receiving thecommunication request signal, sub IC 42 transmits a predetermined signalto driver IC 26, and allows transmitted and received signals to pass. Inthis state, modem 10A1, as shown in FIG. 10, transmits to modem 10A2 adata signal DS of the video signal, which has been received fromintercom 109.

Upon receiving the data signal DS, modem 10A2 transmits an ACK(acknowledgement reply) to modem 10A1. Upon receiving the ACK, modem10A1 transmits a following data signal DS. Modem 10A2 transmits thereceived data signal DS to telephone 103 via LAN cable 9. As a result,the video image captured by intercom 109 is displayed on the telephone103 display. As previously described, since data communication isperformed in data signal band BW2, data communication using in-homecommunication method A is, as shown in FIG. 7 (a), performed in thefrequency band of 3-30 MHz during control period Tc (T2).

At time t9, it is assumed that the user operates TV 102 (see FIG. 1) toreplay motion data, which are stored in server 105 (see FIG. 1). TV 102then transmits a signal of requesting the motion data to modem 10B1 viaLAN cable 9. Upon receiving the signal, modem 10B1, as shown in FIG. 7(a), outputs at time t10 a request signal RS to power lines 2. Duringcontrol period Tc (T2) between times t9 and t10, other modems 10 outputno request signal RS. As a result, modem 10B1 detects no request signalRS from other modems 10, and therefore performs data communication usingthe following entire control period Tc (T3). At time t11, modem 10B1outputs a synchronization signal SS, and then transmits a signal ofrequesting the motion data to server 105 via modem 10B2. Upon receivingthe request signal, server 105 transmits a data signal DS of a videosignal to modem 10B1, after which the motion picture stored in server105 is displayed on TV 102. In other words, data communication usingin-home communication method B is performed, as shown in FIG. 7( a), inthe frequency band of 3-30 MHz during control period Tc (T3), as withthe case of communication method A.

Next, it is assumed that PC 101 (see FIG. 1) transmits to an ISP (notshown) a signal of requesting, for instance, HTML (Hyper Text MarkupLanguage) data. Upon receiving the request signal from PC 101, anddetecting a synchronization signal SS output at time t11, modem 10C1outputs a request signal RS to power lines 2 at time t14. Since othermodems 10 output no request signal RS, modem 10C1 performs datacommunication using the entire following control period Tc (T4). Aftermodem 10C1 transmits a request signal to modem 10C3, modem 10C3 requestsa Web (World Wide Web) server (not shown) of the ISP to send the HTMLdata via fiber cable 8 (see FIG. 1). Upon receiving the HTML data, modem10C3 sends the HTML data to PC 101 via modem 10C1, after which the HTMLdata are displayed on PC 101. In other words, data communication usingaccess communication method C is performed, as shown in FIG. 7( a), inthe frequency band of 3-30 MHz during control period Tc (T4), as withthe case of communication methods A and B.

At time t20, modem 10B1 outputs a synchronization signal SS. Duringcontrol period Tc (T4), however, none of modems 10 outputs a requestsignal RS. Therefore, no data communication is performed during controlperiod Tc from time t30. Modem 10B1 outputs a synchronization signal SSduring each control period Tc. When any modem 10 outputs a requestsignal RS, one of the modems 10B1 performs data communication using thefollowing control period Tc.

As described above, in the first embodiment, different phase vectors areused for a synchronization signal SS and a request signal RS. Therefore,each modem 10 can easily detect a request signal RS output from anothermodem 10 based on a synchronization signal SS without performingrelatively cumbersome modulation and other processes. This allows aplurality of types of modems 10 using different communication methods onthe common power lines 2 to easily coexist. Particularly, for power linecommunication that has a great amount of co-relational noise on the timeaxis, each communication apparatus can perform data communication whileavoiding interference between signals.

In the above-described first embodiment, descriptions have been providedfor the case where the number of time slots is 8 as shown in FIG. 9.However, the number does not need to be 8, and can be arbitrary as longas it is 2 or more. Also, descriptions have been provided for the casewhere each time slot is pre-allocated to its corresponding communicationmethod. However, a corresponding correlation does not need to bepredetermined. When a modem is newly installed to the network, forinstance, it is possible to monitor the output status of a requestsignal RS; and, when a vacant time slot is detected (e.g., when a timeslot in which no request signal RS is output during a predeterminedperiod is detected), the detected time slot can be used.

In the above-described first embodiment, a case has been described wheredata communication is performed using one communication method duringone control period Tc. However, data communication can also be performedusing a plurality of communication methods during one control period Tc.

Descriptions are provided, with reference to FIG. 7 (b), for the casewhere data communication is performed by employing timed division, usinga plurality of communication methods during one control period Tc.Operations between times t1 and T11 in FIG. 7 (b) are identical to thosedescribed in FIG. 7 (a), and their descriptions are thus omitted. Modem10A1 outputs a request signal RS at time t12; and, modem 10B1 outputs arequest signal RS at time t13. Each modem 10 detects, from the requestsignal RS detected during one control period Tc, the number ofcommunication methods of modems 10 that perform data communication. Morespecifically, modems 10A1 and 10B1 detect the request signal RS in timeslot T12 corresponding to communication method A (see FIG. 9), and therequest signal RS in time slot T13 corresponding to communication methodB. On the other hand, modems 10A1 and 10B1 detect no request signal RSin other time slots T14, T15, . . . , T18. As a result, modems 10A1 and10B1 detect that the number of communication methods is two, i.e.,communication methods A and B.

PLC PHY 22B of each modem 10 divides, based on the number ofcommunication methods, time domains during control period Tc for datacommunication. in this example, the order of the divided time domains isset as communication methods A→B. Accordingly, PLC PHY 22B of modem 10A1sets its time domain so that its data communication is performed betweentimes t20 and t21. On the other hand, PLC PHY 22B of modem 10B1 sets itstime domain so that its data communication is performed between timest21 and t30. As a result, data communication using communication methodA and data communication using communication method B are performedbased on time division during control period Tc (T4) as shown in FIG. 7(b).

The following describes, with reference to FIG. 7 (c), a case where datacommunication is performed by employing frequency division, using aplurality of communication methods during one control period Tc. In FIG.7 (c), operations between times t1 and t11 are identical to thosedescribed in FIG. 7 (a), and their descriptions are thus omitted. Modem10B1 outputs a request signal RS at time t13; and modem 10C1 outputs arequest signal RS at time t14. On the other hand, during control periodTc (T4), other modems 10 output no request signal RS. As a result,modems 10B1 and 10C1 detect that the number of communication methods istwo, i.e., communication methods B and C.

PLC PHY 22B of each modem 10 divides, based on the number ofcommunication methods, frequency domains during control period Tc fordata communication. In this example, the in-home system is set in a highfrequency band within data communication band BW2; and the access systemis set in a low frequency band within data communication band BW2. As aresult, PLC PHY 22B of modem 10B1 sets its frequency domain so that itsdata communication is performed in the high frequency band within datacommunication band BW2 via band-pass filters 25 and 29. PLC PHY 22B ofmodem 10C1, on the other hand, sets its frequency domain so that itsdata communication is performed in the low frequency band within datacommunication band BW2 via band-pass filters 25 and 29. As a result,data communication through communication method B and data communicationthrough communication method C are performed based on frequency divisionduring control period Tc (T4) as shown in FIG. 7 (c). As for a systemsuch as the access system having a long transmission line, components ina high frequency band have relatively high attenuation. Therefore, theentire frequency spectrum can be more efficiently used by allocating theaccess system to a low frequency band.

As previously described, at least one of a time domain and a frequencydomain for data communication is set based on the number ofcommunication methods, and data communication is performed using the setdomain. Therefore, each modem 10 can perform data communication whileavoiding interference between data signals.

Second Embodiment

The second embodiment is described in the following with reference toFIGS. 1, 2, and 11 through 14.

Communication system 100 according to the second embodiment is identicalto that described in the first embodiment, and its descriptions are thusomitted. The communication apparatus according to the second embodimentis the same modem 10 described in the first embodiment, and itsdescription are thus omitted.

FIG. 11 is a block diagram illustrating a hardware example thatconstitutes modem 10 according to the second embodiment. Modem 10, asshown in FIG. 11, lacks sub IC 42, which is described in FIG. 3. Modem10, as shown in FIG. 11, further lacks AFE IC 43, band-pass filters 45and 49, and driver IC 46 (hereinafter these are referred to as “AFEcircuit” that have been described in FIG. 3). In other words, modem 10has the same components as described in the first embodiment except forthe deleted sub IC 42 and AFE circuit, and its descriptions are thusomitted. Main IC 22 of FIG. 11 also has the function of sub IC 42 ofFIG. 3. Therefore, PLC PHY block 22B of main IC 22 has the respectivecomponents described in FIG. 4, and its descriptions are thus omitted.

The following describes an example of a specific operation of modem 10according to the second embodiment with reference to FIGS. 11 and 12.FIG. 12 (a) is a time chart that employs frequency division; and FIG. 12(b) is a time chart that employs frequency and time divisions.

First, descriptions are provided for an operation example shown in FIG.12 (a). In this example, the operation is different from that describedin the first embodiment. The same frequency band is used as sharedfrequency band BW1, BW21, BW2 for both transmitting a control signal andperforming data communication. When the frequency band for performingpower line communication is set between 2 and 30 MHz, for instance, theshared frequency band BW1, BW2 is set between 2 and 30 MHz. The sharedfrequency band BW1, BW2 can be changed to different from the frequencyband for use.

At time t41, PLC PHY block 22B of modem 10B1 outputs a synchronizationsignal SS to power lines 2 via band-pass filter 25, the synchronizationsignal SS being set in the shared frequency band BW1, BW2. At time t42,PLC PHY block 22B of modem 10A1 outputs a request signal RS usingband-pass filter 25, as with the synchronization signal SS, the requestsignal RS being set in the shared frequency band BW1, BW2. At time t43,PLC PHY block 22B of modem 10B1, as with modem 10A1, outputs a requestsignal RS, which is set in the shared frequency band BW1, BW2.

In the second embodiment, as with the first embodiment, a period betweentwo adjacent synchronization signals SS is set as one cycle. As shown inFIG. 12, however, one cycle is divided into control period Tc (T21) andits following data period Td. In other words, a control signal and adata signal are time-divided, unlike the first embodiment. Further, asshown in the example shown in FIG. 12 (a), data period Td istime-divided into a plurality of data periods T22, T23, T24, . . . .

More specifically, modem 10A1 performs data communication between timest49 and t50 in the shared frequency band BW1, BW2 during the first dataperiod T22; and modem 10B1 performs data communication between times t50and t51 in the shared frequency band BW1, BW2. Modem 10A1 performs datacommunication between times t51 and t52 during the second data periodT23; and modem 10B1 performs data communication between times t52 andt53. Modem 10A1 performs data communication between times t53 and t54during the third data period T24; and modem 10B1 performs datacommunication between times t54 and t55.

As described above, in the second embodiment, the same frequency band isused for transmitting a control signal and for performing datacommunication. Therefore, as described in FIG. 3 of the firstembodiment, sub IC 42 and AFE circuits can be omitted. Thisconfiguration makes it possible to avoid a large-scale circuitmodification so that a plurality of modems 10 can coexist on the commonpower lines 2.

Although time division has been described in the above-described secondembodiment, frequency division can also be employed. Time division andfrequency division can also be combined. A case where both time andfrequency division are combined is described in the following withreference to FIG. 12 (b).

For instance, when each modem 10 detects a request signal RS from onlythe in-home system during control period Tc, data communication isperformed using time division between different communication methods aswith FIG. 12 (a). Next, as shown in FIG. 12 (b), when each modem 10detects communication methods A, B and C, namely, request signals RSfrom both in-home and access systems, in-home communication methods Aand B perform data communication by employing time division; and accesscommunication method C performs data communication by employingfrequency division. In this case, modems 10A1 and 10B1 using the in-homesystem perform data communication by narrowing the frequency band of2-30 MHz used for transmitting control signals to, for instance, thefrequency band of 3-30 MHz so that data communication can be achieved inthat narrowed frequency band. On the other hand, modem 10C1 using theaccess system performs data communication in the vacant frequency bandof 2-3 MHz. In this case, since different frequency bands are used fortransmitting control signals and data signals DS, each modem 10 may havethe hardware configuration described in FIG. 3.

In addition, FIG. 12 (b) is a mere example of a combination of timedivision and frequency division, and a different combination can also beused. For instance, when there are a plurality of communication methodsusing the access system, data communication can be performed by usingtime division among the communication methods using the access system.It is also possible to use time division as a multiple-access method forthe in-home and access systems, while using frequency division withineach of the in-home and access systems. Further, it is possible todetermine whether to use time division or frequency division as itscommunication method on the basis of which time slot is to be used.

Further, in the above-described second embodiment, descriptions havebeen provided for the case where control signals are all transmitted inthe same frequency band. However, it is also possible to use differentfrequency bands for transmitting different control signals. FIG. 13 is atime chart illustrating an operation example of a plurality of modems10, when different request signals are transmitted. In this case, acontrol signal using the in-home system uses the frequency band of 2-30MHz; and a control signal using the access system uses the frequencyband of 2-3 MHz. In-home data communication uses the frequency band of3-30 MHz, which is different from the band used for transmitting controlsignals. Access data communication, on the other hand, uses thefrequency band of 2-3 MHz, which is the same as the band used fortransmitting control signals. This way (for the purpose of reducing thecircuit size, for instance), a communication method using a narrowfrequency band only can prevent the circuit size from being large.

In the first and second embodiments described above, a case has beendescribed where all the communication methods are in sync withsynchronization signals SS. However, it is also possible not tosynchronize some communication methods. FIG. 14 is a time chartillustrating an operation example of a plurality of modems 10, when somecommunication methods are not in sync with synchronization signals.

In the FIG. 14 example, it is necessary to transmit/receive a requestsignal RS not in sync with a synchronization signal SS. Othercommunication methods need to detect a carrier of a request signal RS ofcommunication method C, the request signal RS being transmitted/receivedasynchronous with a synchronization signal SS. When the carrier isdetected, it is necessary to narrow the frequency band used for thesynchronization signal SS and the request signal RS so that both signalsdo not interfere with communication method C. A communication method insync with the synchronization signal SS can recognize whichcommunication method uses power lines 2 in what form in each time slot.

It is possible to recognize communication methods asynchronous with eachother by receiving asynchronous request signals. However, consideringthe condition of the transmission line as described in FIG. 8 (b), theremay be a case where it is impossible to tell whether a request signalRS, which is in a broad band for a communication method (which can be ina receiving mode), appears to be concentrated in a lower frequency band,affected by the characteristics of the transmission line, or the requestsignal RS is originally set in the lower frequency band only. To preventthis, the phase vector of a request signal RS for synchronouscoexistence and the phase vector of a request signal RS for asynchronouscoexistence are set differently, so that it becomes possible torecognize whether it is the request signal RS in a broad band or therequest signal RS in an originally narrow band. It is still impossibleto recognize, through an asynchronous communication method, acommunication method in sync with a synchronization signal SS. However,asynchronous communication methods can coexist by employing a coexistentmethod using frequency division even when a synchronous communicationmethod can not be recognized.

Affected by the transmission lines as power lines 2, even when therequest signal RS in the broad band and the request signal RS in thenarrow band cannot be differentiated, it has been described that bothsignals can be differentiated by using different phase vectors. However,it is possible to differentiate both signals by determining whether ornot request signals RS are detected synchronously with respect tosynchronous and asynchronous types.

In the above-described first and second embodiments, a synchronizationsignal SS can be generated in any form, as long as it is repeatedlyoutput during a predetermined period. For instance, commercialalternating current voltage AC (or current) on power lines 2 can be usedto generate a synchronization signal SS. In this case, for instance, azero cross of the commercial alternating current voltage AC is detected,and a synchronization signal SS (e.g., a pulse waveform made ofrectangular waves) is generated using a point where the zero cross isdetected as a reference time. When the commercial alternating currentvoltage AC is 100V, 60 Hz, for instance, a synchronization signal SS isgenerated with 60 Hz as a reference frequency. In this case, a zerocross circuit, which includes a comparator or the like, and is connected(directly or indirectly) to power lines 2, can be installed in modem 10shown in FIG. 3 or 11. Average of plurality of reference timesrepresenting the zero cross may be used for the reference time. Thestable reference time can be set even if the zero cross fluctuates.

In the above-described first and second embodiments, descriptions havebeen provided for the case where modem 10B1, which uses communicationmethod B, outputs a synchronization signal SS. However, it is alsopossible that modems 10, which use other communication methods A and C,output a synchronization signal SS as long as at least one modem 10outputs a synchronization signal SS. Modem 10, which outputs thesynchronization signal SS, can be set in either a fixed or variablemode; further, when the variable mode is selected, its setting can bemade either manually or automatically.

For fixed setting, for instance, modem 10 using a specific communicationmethod can be set as a default to output a synchronization signal SS.For manual variable setting, the user can provide in model 10 aninterface (e.g., a switch) that can control whether or not to output asynchronization signal SS. For automatic variable setting, on the otherhand, modem 10 searches for (listens to) a synchronization signal SS (ora request signal) during at least one control period Tc. When asynchronization signal SS is detected, modem 10 itself does not output asynchronization signal SS. On the other hand, when a synchronizationsignal SS is not detected, modem 10 outputs a synchronization signal SS.This way, priority is given to a synchronization signal SS transmittedfrom modem 10 that has already performed power line communication onpower lines 2. Accordingly, even when the modem 10 is disconnected frompower lines 2, one of the other modems 10 automatically outputs asynchronization signal SS.

In the above-described first and second embodiments, descriptions havebeen provided for the case where the phase vectors of a synchronizationsignal SS and a request signal RS are different, but the phase vectorsof request signals RS are all identical. However, it is also possible toset different phase vectors for request signals RS depending on each ofdifferent communication methods. For instance, when sending a signal oftransmission completion (a completion signal), a new different phasevector can be used for the completion signal. This can build a moreflexible environment where modems 10 can coexist. In other words, eachmodem 10 can identify each other even when request signals RS arerandomly output (namely, regardless of time slots). This reduces timerequired for outputting a request signal RS (namely, control period Tc),and improves communication efficiency of the request signal RS.

Third Embodiment

The third embodiment is described in the following with reference toFIGS. 15 through 17.

Communication system 100 according to the third embodiment is identicalto that described in the first embodiment, and its descriptions are thusomitted. As shown in FIG. 2, the communication apparatus according tothe third embodiment is identical to modem 10 according to the firstembodiment, and its descriptions are thus omitted.

FIG. 15 is a block diagram illustrating a hardware example thatconstitutes modem 10 according to the third embodiment. In the circuitconfiguration shown in FIG. 15, zero cross circuit 63 is provided inmodem 10 described in FIG. 3. The circuit configuration shown in FIG. 15is identical to that described in FIG. 3 except for zero cross circuit63, and PLC PHY block 42D (described later) of sub IC 42. Therefore, thesame components are assigned the same numbers, and their descriptionsare thus omitted.

Zero cross circuit 63 includes bridge connection diode 63 a, resistors63 b and 63 c, DC power 63 e and comparator 63 d. Bridge connectiondiode 63 a is connected to resistor 63 b; and the connected resistor 63b is connected in series to another resistor 63 c. These two resistors63 b and 63 c are connected parallel to an input terminal on one end,which is provided in comparator 63 d. A plus side of DC power 63 e isconnected to an input terminal on the other end, which is provided incomparator 63 d. PLC MAC block 42C of sub IC 42 is connected to anoutput terminal, which is provided in comparator 63 d.

FIG. 16 is a functional block diagram of PLC PHY block 42D of sub IC 42.PLC PHY block 42D performs FFT (Fast Fourier Transform) astime-frequency transform. In other words, PLC PHY block 42D includes FFTtransformer 411 and IFFT (Inverse Fourier Transform) transformer 420instead of wavelet transformer 401 and inverse wavelet transformer 410as described in FIG. 4. In the functional block described in FIG. 16,the components common to those of FIG. 4 are assigned the same numbers,and their descriptions are thus omitted. Time-frequency transform doesnot need to be FFT transform, but can also be wavelet transformdescribed in the first and second embodiments.

The following describes an example of a specific operation of modem 10according to the third embodiment with reference to FIGS. 15 through 17.FIG. 17 is a time chart illustrating an operation example of a pluralityof modems 10 according to the third embodiment. The operation shown inFIG. 17 is different from that shown in FIG. 14 only in thatsynchronization is executed in accordance with commercial alternatingcurrent voltage AC, and request signals RS have different phase vectors.In FIG. 17, the operations common to those shown in FIG. 14 are assignedthe same numbers, and their descriptions are thus omitted. Commercialalternating current voltage AC shown in FIG. 17 indicates “voltage” onthe vertical scale, for the sake of easy understanding. The followingdescribes a case where commercial alternating current voltage AC isindicated in the time chart, as shown in FIG. 17. Further, in FIG. 17,60 Hz is indicated as commercial alternating current voltage AC, butother voltage values, for instance, 50 Hz, can also be used.

In this example, each modem 10A1, 10A2, 10B1, 10B2, . . . has itspredetermined phase vector set differently, depending on a frequencyband used for a request signal RS. Communication methods A and B use theentire frequency band of 2-30 MHz (of 2-30 MHz). Communication method Cuses the frequency band of 2-16 MHz (of 2-30 MHz). Arbitrary frequencyband can be used for transmitting a request signal RS.

Each modem 10 is designed to transmit a request signal RS and performdata communication using as a reference point: a zero cross point(voltage is 0 VAC) of commercial alternating current voltage AC in zerocross circuit 63. In this case, 2 AC cycle is considered as one cyclefrom the zero cross of the commercial alternating current voltage AC;and time slots for outputting a request signal RS are set, starting atthe zero cross, in the order of communication methods A, B and C.

At time t42, zero cross circuit 63 of modem 10A1 detects the zero crossZC of the commercial alternating current voltage AC. When the zero crossZC is detected, controller 405 of PLC PHY block 42D of modem 10A1retrieves data related to a phase vector from memory 33. The datarelated to the phase vector indicates phase vector PV1. Morespecifically, PV1 includes rotation degree coefficients which are madeof two values, i.e., 0 and π, corresponding to each sub-carrier, orphase shift values to cyclically shift the sub-carriers with thesecoefficients. Phase rotator 408 of PLC PHY block 42D rotates the phasevector of each of the sub-carriers constituting a multi-carrier signal,by phase vector PV1. IFFT transformer 420 of PLC PHY block 42D performsIFFT transform on the phase-rotated multi-carrier signal in order togenerate a request signal RS. IFFT transformer 420 outputs the generatedrequest signal RS to power lines 2 via AFE IC 43, band-pass filter 45,driver IC 46, coupler 27, power connector 12 and plug 3.

As with modem 10A1, modem 10B1 detects zero cross ZC in zero crosscircuit 63 at time t42. When zero cross ZC is detected, controller 405of PLC PHY block 42D of modem 10B1 retrieves data related to a phasevector from memory 33. Since communication methods A and B use the samefrequency band for transmitting a request signal RS, the data related tothe retrieved phase vector indicates phase vector PV1 as with modem10A1. Phase rotator 408 of PLC PHY block 42D rotates, based on theretrieved phase-vector-related information, the phase vector of eachsub-carrier constituting a multi-carrier signal, by phase vector PV1 aswith modem 10A1. IFFT transformer 420 of PLC PHY block 42D performs IFFTtransform on the phase-rotated multi-carrier signal in order to generatea request signal RS. At time t43, IFFT transformer 420 outputs thegenerated request signal RS to power lines 2, using the detected zerocross as a reference point, in the time slot set for communicationmethod B.

As with modem 10A1, modem 10C1 detects a zero cross ZC in zero crosscircuit 63 at time t42. Upon detecting the zero cross ZC, controller 405of PLC PHY block 42D of modem 10C1 retrieves, from memory 33, datarelated to a phase vector indicating phase vector PV2, which isdifferent from phase vector PV1, since communication method C uses afrequency band different from communication methods A and B fortransmitting a request signal RS. Phase rotator 408 of PLC PHY block 42Drotates the phase of each sub-carrier constituting a multi-carriersignal, by phase vector PV2, based on the data related to the retrievedphase vector, unlike modems 10A1 and 10B1. IFFT transformer 420 of PLCPHY block 42D performs IFFT transform on the phase-rotated multi-carriersignal in order to generate a request signal RS. At time t44, IFFTtransformer 420 outputs the generated request signal RS to power lines2, using the detected zero cross as a reference point, in the time slotset for communication method C.

The following describes a process of detecting a request signal RSperformed by modem 10 with reference to FIGS. 16 to 18. FIG. 18 is aflowchart illustrating a process of detecting a request signal RS. FFTtransformer 411 of PLC PHY block 42D of modem 10 performs FFT transformon a received signal (step S11). Controller 405 of PLC PHY block 42Dretrieves, from memory 33, data related to phase vector PV1. Phaserotator 402 of PLC PHY block 42D rotates the phase of each sub-carrierby referring to the data related to phase vector PV1 and multiplying theFFT-transformed received signal by phase vector PV1 (step S12).

Controller 405 of PLC PHY block 42D makes a quadrant determination onthe phase rotated sub-carriers (step S13) as specifically described inthe following. In this example, it is assumed that 512 sub-carriers areused, and phase vectors on the transmitting and receiving sides are aplurality of coefficients, which indicate rotation degrees (e.g., π, 0,π, π, . . . , 0) corresponding to sub-carrier numbers 1,2,3,4, . . . ,512.

A request signal RS includes known transmitted data as known data, suchas a preamble. The transmitted data correspond to sub-carrier numbers1,2,3,4, . . . , 512. Although known transmitted data can be arbitrary,all of the data are set as “1” in this example. “1” represents (1, 0) onthe complex coordinate plane. Accordingly, the known data are in theform of 1,1,1,1, . . . , 1, which correspond to sub-carrier numbers1,2,3,4, . . . , 512. Phase rotator 408 on the transmitting sidemultiplies the known data 1,1,1,1, . . . , 1 by the phase vectors (π,0,π, π, . . . , 0), and outputs request signals RS having −1,1,−1,−1, . .. 1 as transmitted data to power lines 2.

Phase rotator 402 on the receiving side respectively multipliestransmitted data −1,1,−1,−1, . . . , 1 by coefficients (π,0, π, π, . . ., 0), each of the transmitted data being included in each sub-carrier ofthe transmitted request signal RS. As a result, known data in the formof transmitted data 1,1,1,1, . . . , 1, are re-rotated. Controller 405determines whether the transmitted data indicated by the phase-rotatedsub-carriers are known data such as a preamble. In this case, controller405 sums up the transmitted data, and compares with predeterminedthreshold Th1. For instance, when threshold Th1 is “258” and thetransmitted data are presumably correct, integration value SUM is “512(=1+1+1+1+ . . . +1)”. Therefore, controller 405 determines thatintegration value SUM has exceeded threshold Th1 (step S13: YES). Upondetermining that integration value SUM has exceeded threshold Th1,controller 405 determines that a carrier with phase vector PV1 has beendetected (step S14), and terminates the process. In other words, thereceived signal is a multi-carrier signal whose phase vector is PV1. Onthe other hand, when integration value SUM has not exceeded thresholdTh1, controller 405 determines that integration value SUM has notexceeded threshold Th1 (step S13: NO).

Upon determining that integration value SUM has not exceeded thresholdTh1, controller 405 retrieves, from memory 33, data related to phasevector PV2. Phase rotator 402 of PLC PHY block 42D multiplies theFFT-transformed received signal by phase vector PV2 and rotates thephase of each sub-carrier (step S15). Controller 405 of PLC PHY block42D makes a guardant determination on the phase-rotated sub-carriers(step S16) as with step 13. Upon determining that integration value SUMhas exceeded threshold Th2 (step S16: Yes), controller 405 determinesthat a carrier with phase vector PV2 has been detected (step S18),thereby terminating the process. In other words, the received signal isa multi-carrier signal whose phase vector is PV2. The guardantdetermination is described in detail later.

On the other hand, upon determining that integration value SUM has notexceeded threshold Th2 (step S16: No), controller 405 determines thatthe received signal has neither phase vector PV1 nor PV2 (that it, thesignal is a multi-carrier signal whose phase vector is other than PV1and PV2, or is noise) (step S17), and determines that no carrier withphase vectors PV1 and PV2 has been detected (step S18), therebyterminating the process. It is also possible to perform steps 15 and 16before steps 12 and 13 in FIG. 18. The phase vector does not need to betwo types, i.e., PV1 and PV2, but can be three types or more.

Here, it is assumed, for instance, that the transmission status of thepower line has been deteriorated and a gain in the frequency band of16-30 MHz has become lower. In this case, request signals RS output frommodems 10A1 and 10B1 suffer a higher S/N ratio of sub-carriers, whichare transmitted in the frequency band at or higher than 16 MHz. Thismakes it difficult to differentiate request signals RS output frommodems 10A1 and 10B1 from request signals RS output from modem 10C1.However, since different phase vectors are set for modems 10A1, 10B1 and10C1, request signals RS can be smoothly differentiated from each otherwhen each modem 10 performs the above-described process of detecting arequest signal RS.

As described above, in the third embodiment, different phase vectors areused in accordance with frequency bands used for a request signal RS. Asa result, it becomes possible to differentiate request signals RS evenwhen the transmission status of the power line is deteriorated.

Fourth Embodiment

Communication system 100 according to the fourth embodiment is identicalto that described in the first embodiment, and its descriptions are thusomitted. The communication apparatus according to the fourth embodimentis identical to modem 10 according to the first embodiment as shown inFIG. 2, and its descriptions are thus omitted. The circuit configurationof modem 10 according to the fourth embodiment is identical to that ofFIGS. 15 and 16, and its descriptions are thus omitted.

The following describes an example of a specific operation of modem 10according to the fourth embodiment with reference to FIGS. 19 and 20.FIG. 19 shows time slots corresponding to request signals according tothe fourth embodiment; and FIG. 20 is a flowchart illustrating a processof detecting a request signal according to the fourth embodiment. FIG.19 has extended control period Tc shown in FIG. 17. In the fourthembodiment, which differs from the third embodiment, different phasevectors are set for respective time slots T11, T12, . . . , T17. It isalso possible that different phase vectors are used for differentfrequency bands for use and for different time slots. The number of timeslots is arbitrary as long as it is two or more.

Detailed descriptions are provided in the following. It is assumed thatvarious electric appliances (not shown) are respectively connected tooutlets 5, to which modems 10A1 and 10B1 are connected. In this case,affected by the electric appliances (e.g., impedance variation),commercial alternating current voltage AC2 at outlets 5, to which modems10A1 and 10B1 are connected, incurs a time-lag from commercialalternating current voltage AC1 at outlets 5, to which other modems10C1, . . . are connected. FIG. 19 (a) shows a waveform of commercialalternating current voltage AC1 at the outlets, to which other modems10C1 . . . are connected, while FIG. 19 (b) shows a waveform ofcommercial alternating current voltage AC2 at the outlets, to whichmodems 10A1 and 10B1 are connected. Commercial alternating currentvoltage AC2, as shown in FIGS. 19 (a) and (b), is delayed by time TDcompared to commercial alternating current voltage AC1.

In this case, when modem 10A1 outputs a request signal RSa, zero crosscircuit 63 detects a zero cross ZC of commercial alternating currentvoltage AC2. Commercial alternating current voltage AC2 is delayed onlyby time TD compared to commercial alternating current voltage AC1.Therefore, modem 10A1 outputs a request signal RSa at time t421, whichis delayed only by time TD from time t42.

When modem 10B1 outputs a request signal RSb, zero cross circuit 63detects at time t421 a zero cross ZC of commercial alternating currentvoltage AC2 as with modem 10A1. Upon detecting zero cross ZC, modem 10B1outputs a request signal RSb at time t431, which is delayed only by timeTD from time T43,

At this stage, modem 10C1 has performed a process of detecting a requestsignal RS as shown in FIG. 20, and detects the request signals RSa andRSb. The following describes a carrier detection process in time slotT12 with reference to FIG. 20.

FFT transformer 411 of PLC PHY block 42D of modem 10C1 performs FFTtransform on a received signal (step S21). Next, PLC PHY block 42Dretrieves, from memory 33, data related to a phase vector as slot datacorresponding to time slot T12. Memory 33 stores data related todifferent phase vectors corresponding to time slots T11,T12,T13, . . . .In this example, phase vector PV1 is set for communication method A; andphase vector PV2 is set for communication method B. Memory 33 stores thedata related to phase vectors PV1 and PV2 corresponding to time slotsT11 and T12, respectively.

PLC PHY block 42D outputs the current slot data in zero cross circuit 63(step S22). More specifically, modem 10C1 recognizes, from commercialalternating current voltage AC1 in zero cross circuit 63, that a zerocross ZC is at time t42. Each modem 10 includes a counter (not shown)and stores data indicating the time durations of the time slots.Therefore, each modem 10 can specify how many time slots exist betweenthe current time slot and the zero cross ZC by both the elapsed timefrom zero cross ZC and time width of the time slot.

At time t43, for instance, PLC PHY block 42D of modem 10C1 recognizesthat an elapsed time from the zero cross ZC is a time duration per timeslot, and determines that the current time slot is “T12”. As a result,controller 405 of PLC PHY block 42D retrieves, from memory 33, the datarelated to phase vector PV2 corresponding to time slot T12.

Then, phase rotator 402 of PLC PHY block 42D multiplies theFFT-transformed received signal by phase vector PV2, so as to rotate thephase of each sub-carrier (step S23). Phase rotator 405 of PLC PHY block42D makes a quadrant determination on each of the phase-rotatedsub-carriers (step S24) as with steps 13 and 15 described in FIG. 18.Steps S25 and S26 are identical to steps S14 (or S17) and S18, and theirdescriptions are thus omitted.

In time slot T12, the phase vectors of the two request signals RSa andRSb are output as shown in FIG. 19 (a). As described above, however,modem 10C1 rotates the phases of the sub-carriers by phase vector PV2,and thus only detects the request signal RSb.

As described above, in the fourth embodiment, each modem 10 rotates thephases of the sub-carriers of the request signal RS output in the timeslot by the phase vector corresponding to the time slot. This enables areliable detection of request signals RS output in each time slot, evenwhen there is a time difference between alternating current voltagesACs.

In the above-described fourth embodiment, descriptions have beenprovided for the case where different phase vectors are set for timeslots T11,T12, . . . ,T17. However, it is not necessary to set differentphase vectors for respective time slots. Phase vectors can be reliablydifferentiated when phase vectors having different rotation degrees(e.g., PV1 and PV2) are set at least for adjacent time slots (e.g., T11and T12).

Fifth Embodiment

Communication system 100 according to the fifth embodiment is identicalto that described in the first embodiment, and its descriptions are thusomitted. The communication apparatus according to the fifth embodimentis modem 10 described in the first embodiment, and its descriptions arethus omitted. The circuit configuration of modem 10 according to thefifth embodiment is identical to that of FIGS. 15 and 16, and itsdescriptions are thus omitted.

The following describes an example of a specific operation of modem 10according to the fifth embodiment with reference to FIGS. 21 and 22.FIG. 21 is a time chart illustrating an operation example of a pluralityof modems 10 according to the fifth embodiment. FIG. 22 is a flowchartillustrating a process of modifying a phase vector according to thefifth embodiment. The process of detecting a request signal RS isidentical to that described with reference to FIG. 20 in the fourthembodiment.

The following describes a phase vector modification process performed bymodem 10A1. Modem 10A1 searches for a request signal RS during controlperiod Tc (step S31). For instance, it is assumed that controller 405(see FIG. 16) of PLC PHY block 42D of modem 10A1 detects a zero cross ZCin zero cross circuit 63 (see FIG. 15) at time t81 shown in FIG. 21.Controller 405 determines whether or not the request signal RS is outputbetween times t81 and t82. The carrier detection method is identical tothat described in FIG. 18, and its descriptions are thus omitted.

In the fifth embodiment, each time slot during control period Tc isallocated to communication methods in the order of “C”, “A” and “B”.When data communication is performed through communication methods A, B,. . . , data period Td is time-divided into communication methods A, B,. . . . When data communication is performed through communicationmethods A, B, . . . and C, a frequency band of 16-30 MHz is allocated tocommunication methods A, B, . . . ; and a frequency band of 2-16 MHz isallocated to communication method C, thus dividing the frequency bandused for power line communication. Memory 33 of each modem 10 storesdata including these time slot allocations and which multiple-accessscheme is employed when which request signal RS is output.

Modem 10A1 determines whether or not a desired channel has a vacancy(step S32). A channel only needs to be at least one of time andfrequency bands, and a frequency band is used in this example. Whenmodem 10A1 wishes to use the frequency band of 2-30 MHz and when norequest signal RS is output between times t81 and t82, controller 405 ofPLC PHY block 42D of modem 10A1 determines that the desired channel hasa vacancy (step S32:Yes), since communication method C does not performdata communication during the following data period Td (between timest84 and t86), and terminates the process.

Accordingly, modem 10A1 performs data communication using the frequencyband of 2-30 MHz without performing a phase vector modification processat time t84. In this case, since modem 10B1 outputs a request signal RSat time t83, modem 10A1 detects the request signal RS output from modem10B1; and modems 10A1 and 10B1 alternately perform data communicationduring data period Td.

Further, in FIG. 21, the time durations of control period Tc and dataperiod Td are equal to two cycles of commercial alternating currentvoltage AC. However, this is arbitrary as long as it is over ⅙ cycle ofcommercial alternating current voltage AC. Particularly, it ispreferable that ½ cycle be used for a single-phase; and ⅙ or more cyclebe used for three-phases. This is because it eliminates the need todetermine whether commercial alternating current voltage AC is increasedor decreased even when the waveform of the commercial alternatingcurrent voltage AC is inverted by an inverted insertion direction of apair of plug terminals.

Time durations do not need to be equally divided for the data divisionof data communication. For instance, one of the time durations can belonger than the others. Although, in FIG. 21, data communication areperformed three times for one communication method during one dataperiod Td, the number of performing data communication is arbitrary.

At time t86, modem 10A1 starts the process described in FIG. 22, andagain searches for a request signal RS (step S31). At the same time,modem 10A1 determines whether or not a desired channel (frequency band)has a vacancy (step S32). Controller 405 of PLC PHY block 42D of modem10A1 determines whether or not a request signal RS is output betweentime t86 and t87. As shown in FIG. 21, since modem 10C1 outputs arequest signal RS, controller 405 determines that the desired channelhas no vacancy since communication method C performs data communicationduring the following data period Td between times t84 and t86 (step S32:No).

Controller 405 of PLC PHY block 42D of modem 10A1 modifies the phasevector corresponding to the channel (frequency band) (step S32). In thisexample, memory 33 stores the data related to phase vector PV1, whichcorresponds to the frequency band of 2-30 MHz, and the data related tophase vector PV2, which corresponds to the frequency band of 16-30 MHz.Further, phase vector PV1 is set for modem 10A1 as a phase vectorbetween times t81 and t87.

Communication method C performs data communication (since the frequencyband of 2-16 MHz cannot be used) during the following data period Td(between times t86 and t89), controller 405 of PLC PHY block 42D ofmodem 10A1 retrieves, from memory 33, the data related to the phasevector corresponding to the frequency band of 16-30 MHz. In other words,controller 405 retrieves, from memory 33, the data related to phasevector PV2; and phase rotator 408 of PLC PHY block 42D of modem 10A1modifies the phase vector to PV2 (step S32). The phase vectormodification process has been described in detail in the forthembodiment, and its descriptions are thus omitted.

Upon changing the phase vector, IFFT transformer 420 of PLC PHY block42D of modem 10A1 performs IFFT transform on the sub-carriers whosephase vectors are rotated using PV2, so as to generate a transmittedsignal. PLC PHY block 42D of modem 10A1 shuts off the frequency band of2-16 MHz from the transmitted signal by controlling band-pass filter 45.The transmitted signal in the frequency band of 16-30 MHz is output as arequest signal RS to power lines 2 via driver IC 46, coupler 27, powerconnector 12 and plug 3. Modem 10A1 outputs the request signal RSbetween times t87 and time t88 (step S33) and terminates the process.Modem 10B1 performs the same process, whose descriptions are thusomitted. Accordingly, during data period Td starting at time t89, modem10C1 performs data communication in the frequency band of 2-16 MHz; andmodems 10A1 and 10B1 perform data communication in the frequency band of16-30 MHz.

Since modem 10A1 modifies a phase vector according to a frequency bandfor a request signal RS, other modems 10B1, 10C1, . . . can easilyspecify the frequency band used for the request signal RS even when thestatus of the transmission line is deteriorated. The same effects can beobtained when any other modem 10 differentiates the request signal RS.

As described above, in the fifth embodiment, a phase vector is modifiedaccording to a frequency band used for a request signal RS. Therefore,the frequency band used for the request signal RS can be smoothlyspecified despite changes of the transmission line status. As a result,a phase vector can be smoothly recognized even when the condition of thetransmission line is deteriorated.

In the above-described third to fifth embodiments, descriptions havebeen provided for the case where a request signal RS is output at atiming relative to a zero cross as a reference point. However, such atiming does not need to be referenced to a zero cross. For instance, atiming can be arbitrary referenced as long as it is where commercialalternating current voltage AC reaches a predetermined voltage value(e.g., 10V) and it starts at the detected time point.

In the above-described first to fifth embodiments, descriptions havebeen provided for a power line as an example of a transmission line thatperforms transmission of a control signal and data communication.However, a line other than a power line can also be used. For instance,both wireless and wired cables can also be used as transmission lines.For a wired transmission line, for instance, various cables such as acoaxial cable, a telephone line and a speaker line can be used.

In the above-described first to fifth embodiments, a phase vectormodification has been referred to as “rotating the phase of asub-carrier”. This is same as rotating a signal point on the complexcoordinate plane. In addition, “phase vector” defined in thespecification is a set of values indicating a rotation degree by whichthe signal point of each sub-carrier is rotated on the complexcoordinate plane, each sub-carrier constituting a multi-carrier signalsuch as an OFDM signal. “Phase vector” is therefore a combination ofvalues for equalizing time waveforms of the multi-carrier signal(suppressing a peak on the time axis). A phase vector has two types,i.e., a fixed value, which is a combination of predetermined values, anda variable value, which is a combination of varied values according topredetermined conditions. Such predetermined conditions include a cyclicshift and a random value. In addition, a phase vector is also referredto as a “carrier phase”. In this case, a fixed value is referred to as a“deterministic carrier phase”; and a variable value is referred to as a“random carrier phase”. The above-described request signal RS is alsoreferred to as a CDFC (Commonly Distributed Coordination Function)signal.

The above-described first through fifth embodiments are individuallydescribed. However, these embodiments can also be combined as needed.

The communication apparatus and the communication method according tothe present invention are useful for power line communicationparticularly in collective housings such as an apartment and acondominium because of its abilities to communicate while avoidinginterference between signals when a plurality of communicationapparatuses using different communication methods are connected to acommon transmission line.

It is noted that the foregoing examples have been provided merely forthe purpose of explanation and are in no way to be construed as limitingof the present invention. While the present invention has been describedwith reference to exemplary embodiments, it is understood that the wordswhich have been used herein are words of description and illustration,rather than words of limitation. Changes may be made, within the purviewof the appended claims, as presently stated and as amended, withoutdeparting from the scope and spirit of the present invention in itsaspects. Although the present invention has been described herein withreference to particular structures, materials and embodiments, thepresent invention is not intended to be limited to the particularsdisclosed herein; rather, the present invention extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims.

The present invention is not limited to the above described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

This application is based on the Japanese Patent Application Nos.2005-297529 filed on Oct. 12, 2005, and 2006-114191 filed on Apr. 18,2006, entire contents of which are expressly incorporated by referenceherein.

1. A power-line communication apparatus for transmitting a multi-carriersignal including a plurality of sub-carriers to another communicationapparatus through a power line, comprising: a phase rotation sectionconfigured to rotate phase of at least one sub-carrier among theplurality of sub-carriers, by use of a first phase vector or a secondphase vector that differs from the first phase vector; a multi-carriersignal output section configured to output at least one of a firstmulti-carrier signal in which phase of at least one sub-carrier isrotated with the first phase vector, and a second multi-carrier signalin which phase of at least one sub-carrier is rotated with the secondphase vector; a band setting section configured to set up at least oneof a time band and a frequency band, on the basis of at least one of thefirst multi-carrier signal and the second multi-carrier signal, whichare outputted to a power line by the multi-carrier signal outputsection; and a communication section configured to perform communicationwith another communication apparatus through a power line, by use of atleast one of the time band and the frequency band, which are set up bythe band setting section.
 2. The communication apparatus according toclaim 1, further comprising: a frequency band setting section configuredto set up a frequency band that is used in the second multi-carriersignal, wherein, the phase rotation section sets up a rotation amountaccording to the frequency band that is set up by the band settingsection, and changes the first phase vector to the second phase vectorindicating the set rotation amount.
 3. The communication apparatusaccording to claim 1, further comprising: a time point detection sectionconfigured to detect a time point where an alternating voltagetransmitted to the power line reaches a predetermined voltage value,wherein, the multi-carrier signal output section outputs at least one ofthe first multi-carrier signal, and the second multi-carrier signal, byuse of timing based on the time point detected by the time pointdetection section.
 4. The communication apparatus according to claim 1,wherein the multi-carrier signal output section outputs the firstmulti-carrier signal repeatedly to a power line through a predeterminedtime, and outputs the second multi-carrier signal, by use of timingwhere the first multi-carrier signal was outputted.
 5. The communicationapparatus according to claim 1, wherein the phase rotation section setsup a rotation amount by use of a PN sequence, and changes the firstphase vector, to the second phase vector indicating the set rotationamount.
 6. The communication apparatus according to claim 5, wherein thePN sequence is a M sequence.
 7. The communication apparatus according toclaim 1, wherein the multi-carrier signal output section outputs thefirst multi-carrier signal in a first period, and output the secondmulti-carrier signal in a second period that differs from the firstperiod.
 8. An integrated circuit device for transmitting a multi-carriersignal including a plurality of sub-carriers, to another communicationapparatus through a power line, comprising: a phase rotation sectionconfigured to rotate phase of at least one sub-carrier among theplurality of sub-carriers, by use of a first phase vector or a secondphase vector that differs from the first phase vector; a multi-carriersignal output section configured to output at least one of a firstmulti-carrier signal in which phase of at least one sub-carrier isrotated with the first phase vector, and a second multi-carrier signalin which phase of at least one sub-carrier is rotated with the secondphase vector; a band setting section configured to set up at least oneof a time band and a frequency band, on the basis of at least one of thefirst multi-carrier signal and the second multi-carrier signal, whichare outputted to a power line by the multi-carrier signal outputsection; and a communication section configured to perform communicationwith another communication apparatus through a power line, by use of atleast one of the time band and the frequency band, which are set up bythe band setting section.
 9. A communication method for transmitting amulti-carrier signal including a plurality of sub-carriers, to anothercommunication apparatus through a power line, comprising the steps of:rotating phase of at least one sub-carrier among the plurality ofsub-carriers, by use of a first phase vector or a second phase vectorthat differs from the first phase vector; outputting at least one of afirst multi-carrier signal in which phase of at least one sub-carrier isrotated with the first phase vector, and a second multi-carrier signalin which phase of at least one sub-carrier is rotated with the secondphase vector; setting up at least one of a time band and a frequencyband, on the basis of at least one of the first multi-carrier signal andthe second multi-carrier signal, which are outputted to a power line inthe multi-carrier signal outputting step; and performing communicationwith another communication apparatus through a power line, by use of atleast one of the time band and the frequency band, which are set up inthe band setting step.